MOCVD molybdenum nitride diffusion barrier for CU metallization

ABSTRACT

A new method of forming a molybdenum nitride barrier layer by chemical vapor deposition from the precursor bisdiethylamido-bistertbutylimido-molybdenum (BDBTM) as a diffusion barrier for copper metallization is described. Semiconductor device structures are provided in and on a semiconductor substrate. An insulating layer is deposited overlying the sermiconductor device structures. A via opening is etched through the insulating layer to contact one of the semiconductor device structures. A barrier layer of molybdenum nitride is conformally deposited by chemical vapor deposition within the via. A layer of copper is deposited overlying the molybdenum nitride barrier layer wherein the molybdenum nitride barrier layer prevents copper diffusion to complete the copper metallization in the fabrication of an integrated circuit device.

This is a division of patent application Ser. No. 08/985,404, filingdate Dec. 5, 1997, Mocvd Molybdenum Nitirde Diffusion Barrier For CuMetallization, now U.S. Pat. No. 6,114,242, assigned to the sameassignee as the present invention

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The invention relates to a method of barrier layer formation in thefabrication of integrated circuits, and more particularly, to a methodof forming a CVD molybdenum nitride barrier layer to prevent copperdiffusion in the manufacture of integrated circuits.

(2) Description of the Prior Art

In a common application for integrated circuit fabrication, acontact/via opening is etched through an insulating layer to anunderlying conductive area to which electrical contact is to be made. Abarrier layer, typically titanium nitride, is formed within thecontact/via opening. A conducting layer material, typically tungsten, isdeposited within the contact/via opening. As device sizes continue toshrink, these typical material, are no longer adequate. Because of itslower bulk resistivity, Copper (Cu) metallization is the futuretechnology for feature sizes of 0.18 microns and below. Cu metallizationrequires a good diffusion barrier to prevent the copper from diffusingthrough the active junctions. The inventors have found that Molybdenumnitride (MoN) is a good diffusion barrier for Cu.

U.S. Pat. No. 5,646,426 to Cockrum et al discloses a MoN film depositedby reactive sputtering under Indium. U.S. Pat. No. 4,960,732 to Dixit etal teaches a barrier layer of MoN for use with a tungsten plug, U.S.Pat. No. 4,431,708 to Carver et al teaches forming a molybdenum film andannealing it to reduce resistivity. None of the references disclose CVDMoN as a diffusion barrier for Cu.

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide an effectiveand very manufacturable method of forming a molybdenum nitride barrierlayer in a copper metallization process in the fabrication of integratedcircuit devices.

Another object of the invention is to provide a method for forming amolybdenum nitride barrier layer that will prevent copper from diffusinginto active junctions.

A further object of the invention is to provide a method for forming amolybdenum nitride barrier layer by chemical vapor deposition.

A still further object of the invention is to provide a new precursor,bisdiethylamido-bistertbutylimido-molybdenum (BDBTM) for chemical vapordeposition of molybdenum nitride.

Yet another object of the invention is to provide a method for forming amolybdenum nitride barrier layer by chemical vapor deposition from theprecursor bisdiethylamido-bistertbutylimido-molybdenum (BDBTM).

Yet another object of the invention is to provide a method for forming amolybdenum nitride barrier layer by chemical vapor deposition from theprecursor bisdiethylamido-bistertbutylimido-molybdenum (BDBTM) as adiffusion barrier for copper metallization.

In accordance with the objects of this invention a new method of forminga molybdenum nitride barrier layer by chemical vapor deposition from theprecursor bisdiethylamido-bistertbutylimido-molybdenum (BDBTM) as adiffusion barrier for copper metallization is achieved. Semiconductordevice structures are provided in and on a semiconductor substrate. Aninsulating layer is deposited overlying the semiconductor devicestructures, A via opening is etched through the insulating layer tocontact one of the semiconductor device structures, A barrier layer ofmolybdenum nitride is conformally deposited by chemical vapor depositionwithin the via. A layer of copper is deposited overlying the molybdenumnitride barrier layer wherein the molybdenum nitride barrier layerprevents copper diffusion to complete the copper metallization in thefabrication of an integrated circuit device.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings forming a material part of thisdescription, there is shown:

FIGS. 1, 2, 4 and 5 schematically illustrate in cross-sectionalrepresentation a preferred embodiment of the present invention.

FIG. 3 illustrates the molecular structure of thebisdiethylamido-bistertbutylimido-molybdenum (BDBTM) precursor of thepresent invention.

FIGS. 6A and 6B graphically illustrate SIMS depth profiles of theCu/MoN/Si structure of the present invention.

FIGS. 7A and 7B graphically illustrate leakage current densitydistributions of the Cu/MoN/Si p+n junction structure of the presentinvention.

FIG. 8 graphically illustrates growth rate and resistivity of a MoN filmas a function of deposition temperature.

FIGS. 9A, 9B, and 9C graphically illustrate Auger depth profiles of theCu/MoN/Si structure of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now more particularly to FIG. 1, there is illustrated aportion of a partially completed integrated circuit device. There isshown a semiconductor substrate 10, preferably composed ofmonocrystalline silicon. Semiconductor devices structures are formed inand on the semiconductor substrate. For example, a gate electrode 16 anda source/drain region 14 are illustrated in FIG. 1. Source/drain region14 is a P+ region in the illustration, It is well understand by thoseskilled in the art that this could be an N+ region as well. It should beunderstood that the invention is not limited to the embodimentillustrated in the drawing figures, but is applicable to any applicationin which copper metallization is used.

An insulating layer 20, composed of silicon dioxide, borophosphosilicateglass (BPSG), borosilicate glass (BSG), phosphosilicate glass (PSG), orthe like, is deposited over the surface of the semiconductor structuresto a thickness of between about 5000 to 9000 Angstroms and preferablyplanarized.

A contact/via opening 22 is etched through the insulating layer 20 tothe source/drain region 14 within the semiconductor substrate. A gluelayer 24, such as titanium, is deposited over the insulating layer andwithin the via opening to a thickness of about 200 Angstroms. Aftersubsequent heat treatment, the titanium will react with the underlyingsilicon within the via opening to form titanium silicide 26 which willreduce contact resistance. The glue layer is shown in FIG. 2.

The inventors have discovered that molybdenum nitride (MoN) canwithstand Cu diffusion up to 550° C. post processing temperature for 30minutes. This is at least as effective or better than CVD titaniumnitride. MoN deposited by metal organic chemical vapor deposition(MOCVD) has better step coverage than MoN deposited by physical vapordeposition (PVD). The inventors have developed a new precursor fordepositing MoN by MOCVD.

The new precursor, bisdiethylamido-bistertbutylimido-molybdenum (BDBTM),a dark-yellow compound at room temperature, has the molecular structureMo (^(t)BuN)₂ (NE_(t2))₂, illustrated in FIG. 3. The strong Mo=N doublebond preserves the MoN portion of the precursor and results in a cubicphase MoN film during the pyrolysis proccess. The cubic phase has lowerresistivity than other phases.

Using the precursor BDBTM, a MoN layer 28 is deposited by MOCVD withinthe contact/via opening. The precursor BDBTM is flowed at a rate ofbetween about 20 to 40 sccm using argon as a carrier gas at atemperature of between about 450 and 600° C. and pressure of 0.2 to 0.4Torr. The MoN layer 28 is deposited to a thickness of between about 200and 600 Angstroms This layer 28 forms a barrier layer, as illustrated inFIG. 4

The MOCVD process of the invention uses a low deposition temperature ofbetween about 450 to 600° C. for good conformality. In order to lowerresistivity at this low deposition temperature, a post-treatment of theMoN film is implemented.

There are two alternative approaches to the MoN post-treatment. In thefirst approach, after the MoN layer has been deposited to its desiredthickness, the wafer is exposed to NH₃ gas at a temperature of 450 to650° C. for about 30 minutes. In the second approach, 100 Angstroms ofMoN is deposited, for example at 450° C., as the barrier layer 28. Thenthe wafer is exposed to a 50 watt N₂ plasma treatment at 650° C. for 30minutes. Another 100 Angstroms of MoN is deposited, followed by anotherN₂ plasma treatment. The sequence of MoN deposition and N₂ plasmatreatment is repeated until the desired MoN thickness of the barrierlayer 28 is achieved.

Referring now to FIG. 5, a layer of copper 30 is sputter deposited overthe barrier layer 28 to fill the contact/via opening. The copper layerand the barrier layer are patterned to form the desired electricalcontact.

FIGS. 6A and 6B illustrate the barrier property of 600 Angstroms of CVDMoN against copper diffusion, using SIMS Analysis. FIG. 6A illustratesthe depth profile of copper (line 61), MoN (line 62), and silicon (line63) after annealing at 550° C. for 30 minutes. The annealing wasperformed to simulate thermal processing subsequent to the copperdeposition. FIG. 6B illustrates the depth profile of copper (line 66),MoN (line 67), and silicon (line 68) after annealing at 600° C. for 30minutes. It can be seen that at post processing temperatures of 600° C.,the copper penetrated into the silicon by diffusing through the MoNbarrier, but at post processing temperatures of 550° C., the MoN barrierheld against Cu diffusion.

FIGS. 7A and 7B illustrate the p+n junction diode measurements. Theleakage current density distributions are shown, in FIG. 7A, afterannealing at 550° C. for 30 minutes, and in FIG. 7B, after annealing at600° C. for 30 minutes. The leakage current in FIG. 7B is too high, butthe leakage current in FIG. 7A is acceptable. This indicates that MoNcan withstand Cu diffusion at post-processing temperatures of up to 550°C. for 30 minutes.

FIG. 8 illustrates the growth kinetics and film resistivity of the MoNfilm. Line 81 shows the growth rate of the MoN film at differenttemperatures. Growth rate is higher at higher temperatures. Line 82shows that the resistivity of the film is lower at higher temperatures.However, higher temperature deposition results in decreased conformalityof the film. This is a known problem for CVD titanium nitride as well.

FIGS. 9A, 9E, and 9C illustrate the effects of the MoN post-treatment.These figures illustrate the Auger depth profiles of the CVD MoN filmdeposited at 450° C. FIG. 9A illustrates the concentrations of theelements of the film after deposition. High concentrations of carbon 91and oxygen 92 relative to molybdenum 93 and nitrogen 94 result in highresistivity. FIG. 9B illustrates the Auger depth profiles after the 30minute NH₃ treatment of the invention. It can be seen that carbon 91 andoxygen 92 concentrations are reduced, thereby reducing resistance. FIG.9C illustrates the Auger depth profiles after the 30 minute N₂ plasmatreatment of the invention. The carbon 91 and oxygen 92 concentrationshave been reduced further, resulting in decreased resistance.

The process of the invention results in an effective and verymanufacturable MoN diffusion barrier for copper metallization. The newBDBTM precursor of the invention for MOCVD of MoN provides a highquality MoN film with good step coverage.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention.

What is claimed is:
 1. A precursor for forming MoN by chemical vapordeposition, consisting of a compound of the formula: Mo(^(t)BuN)₂(NEt₂)₂wherein a double bond exists between said Mo and each of said (^(t)BuN).2. The precursor according to claim 1 wherein said compound is adark-yellow liquid at room temperature.
 3. A precursor for forming MoNby chemical vapor deposition, consisting of a compound Bis(diethylamido) bis (tertbutylimido) Molybdenum having the formula:


4. The precursor according to claim 3 wherein said compound is adark-yellow liquid at room temperature.